Actuator device with shape-memory flexible cable

ABSTRACT

An actuator including a shape-memory flexible cable with a flexible sheath can be used, by controlling it both electrically and mechanically using the sheath as element for applying a mechanical tensile force. The shape-memory flexible cable is provided with a coating made of synthetic or elastomer material moulded thereon and adherent thereto, which favors rapid return of the shape-memory cable into its resting configuration after its activation both on account of its elastic return and owing to the fact that it favors cooling of the cable. Preferably, the coating is obtained by means of a process of co-extrusion with the shape-memory cable.

BACKGROUND OF THE INVENTION

The present invention relates to an actuator device comprising aflexible cable, which has one end connected to a controlled member, anda flexible sheath, inside which is mounted the flexible cable, in whichat least one portion of the flexible cable consists of a shape-memorymaterial, which is able to undergo a variation of shape following uponits heating, in order to control the controlled member.

Flexible-cable actuator devices find their application in a wide rangeof fields and in general wherever it is necessary to provide amechanical transmission which is simple and inexpensive and will enableremote control of the displacement of a member. Flexible-cable actuatordevices are, for example, used for providing manual-control actuationson motor vehicles, for example for release from inside of the rearhatchback or of the bonnet, or for actuation of mobile parts or ofmechanisms of seats of motor vehicle, or for the actuation of mobilemembers of the engine or of facilities on board the motor vehicle. Thereis moreover known a wide range of applications also outside theautomobile field.

A flexible-cable actuator device having the characteristics referred toat the start of the present description is known from the documentDE-C-199 16 244. Said known device is designed to be controlled manuallyin all conditions of use. However, its actuation brings about anactivation of the shape-memory element, with the consequence that thecontrolled member undergoes an additional displacement with respect tothe one brought about by mere manual actuation.

In the prior Italian patent application No. TO2001A000618, filed on Jun.27, 2001, and in the corresponding internal patent applicationPCT/IB02/02361, the present applicant has proposed an actuator devicecomprising:

-   -   a flexible cable having one end connected to a controlled        member, and    -   a flexible sheath inside which is mounted the flexible cable,    -   in which at least one portion of the flexible cable consists of        a shape-memory material which is able to undergo a variation of        shape following upon its heating in order to control the        controlled member,    -   in which the aforesaid sheath is mounted with respect to a fixed        supporting structure so as to be free to be displaced        longitudinally only in a direction corresponding to the        direction of actuation of the controlled member, and    -   in which, moreover, the aforesaid sheath is coupled to the        controlled member so as to be able to transmit directly thereto        a displacement in the aforesaid direction of actuation and to        be, instead, uncoupled by the controlled member in the event of        a movement in the opposite direction, in such a way that said        actuator is able to be used both manually, as element of        mechanical transmission, using the sheath as element of        transmission, and exploiting the variation of shape of the        shape-memory cable, which can be obtained with its heating. The        heating can be obtained by causing passage of electric current        through the shape-memory cable.

SUMMARY OF THE INVENTION

With the purpose of further improving the actuator device describedabove, the subject of the present invention is a device having all thecharacteristics referred to above and characterized in that saidflexible cable is provided with a coating of elastomer or syntheticmaterial moulded thereon and adherent thereto, which is elasticallydeformed when the shape-memory cable is activated, so as to favourreturn of the shape-memory cable to its resting position both thanks toits elastic return, and in so far as its accelerates cooling of theshape-memory cable after activation.

Preferably said coating is obtained by means of an operation ofsimultaneous extrusion (co-extrusion) together with the shape-memorycable.

It should be noted that the coating thus obtained adheres to the cableand constitutes a separate element both with respect to the sheath ofthe actuator device and with respect to possible further spacercoatings, which are also illustrated in the preceding patent applicationof the present applicant, set between the cable and the sheath.

The material of the coating co-extruded on the cable is chosen so as toenable a dual advantage to be obtained. On the one hand, said materialis not an electrical conductor, so that it will not heat up, as,instead, the cable does heat up when the latter is traversed by electriccurrent during activation of the actuator. Consequently, the material ofthe aforesaid co-extruded coating favours and accelerates the cooling ofthe shape-memory cable at the end of the activation step. A secondimportant advantage lies in the fact that since the aforesaid coating ismade of elastic material it acts as a distributed spring that undergoesa compressive stress when the cable made of shape-memory material isshortened following upon its activation. Consequently, the coatingcontributes to a rapid return of the cable into the resting condition,at the end of an activation step, not only in so far as it acceleratescooling, but also in so far as it pushes the cable towards its restingcondition as a result of its elastic return.

Of course, the invention is of general application and can consequentlybe used also outside the automobile sector, and in particular in anysector where it may prove useful to apply an actuator device that can beactuated both manually and electrically. Shape-memory actuator elementshave been known for some time and used in a wide range of fields inwhich it is necessary to have available actuator means of simple andlow-cost structure. They use shape-memory metal alloys capable of beingdeformed following upon overstepping of a pre-determined transitiontemperature. In general, heating can be obtained by the actuator elementdetecting directly a variable temperature, or else by supply of anelectric current through the actuator element so as to heat it by theJoule effect. In the case of the invention, the electrical-supply meanscan be associated to electronic-control means designed for controllingsupply of electric current according to a signal detected by atemperature sensor, by a position or displacement sensor or by apotentiometer.

Of course, the configuration of the cable made of shape-memory materialcan be any whatsoever. In particular, the cable can also have a U-shapedconfiguration, with a forward stretch and a return stretch, and its twoends set adjacent to one another, or else again it is possible toprovide a plurality of cables co-extruded inside one and the samecoating material.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to the annexeddrawings, which are provided purely by way of non-limiting example andin which:

FIG. 1 is a partially sectioned perspective view of an embodiment of theactuator device previously proposed by the present applicant,corresponding to FIG. 5 of the international patent applicationPCT/IB02/02361 mentioned above; and

FIG. 2 is a partial and partially sectioned perspective view of thecable forming part of the actuator device according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, there is here illustrated an example ofapplication of the actuator previously proposed for control of the lockof a rear hatchback of a motor vehicle.

There exist standards that impose on the manufacturer the need toprovide for the possibility of manual operation of the lock from insidein order to enable the opening of the hatchback for a person who were toremain accidentally closed inside the motor vehicle. In the exampleillustrated, the actuator can be operated manually by means of a ring100 that is connected via a cable 101 to the sheath 3 of aflexible-cable actuator device. Secured on the sheath 3 is a bushing102, which is designed to come to bear upon a fixed arrest 103 formingpart of the structure 104 of the device of the hatchback lock. Thecooperating action of the bushing 102 fixed to the sheath 3 and of thearrest 103 prevents a displacement of the sheath 3 in a directionopposite to the direction of actuation. Inside the sheath 3 is set aflexible cable 2 made of shape-memory material, which is secured, at oneend 2a, to a cylindrical body 5, which is in turn connected, through aslit 105 made in the wall of the shell of the lock 104, to thecontrolled member of the lock (not illustrated). Also provided are meansof electrical supply (not illustrated) for applying a voltage to the twoopposite ends of the shape-memory cable 2 in order to bring about itsshortening. When the actuator is operated manually by acting on the ring100, the mechanical tension is transmitted through the sheath 3, whichis displaced to the right (as viewed in FIG. 1), causing a recession ofthe bushing 102 away from the fixed arrest 103. The displacement of thesheath 3 causes a corresponding displacement of the cylindrical body 5since anchored to the end of the sheath 3 is a ring 11 that bears uponan end surface 5a of an internal cavity of the cylindrical body 5. Thedisplacement of the latter causes an actuation of the controlled member,which, as already mentioned, is connected to the cylindrical body 5 bymeans of a connection passing through the slit 105.

In the case, instead, of electrical actuation, the sheath 3 remainsstationary, since it is not able to displace to the left as a result ofthe engagement of the bushing 102 against the fixed arrest 103, whilstthe shape-memory cable 2 is shortened, causing a sliding of the cylinder5 over the sheath 3 (so that the ring 11 is moved away from the contrastsurface 5a) and again an actuation of the controlled member.

The advantage of using the sheath of the actuator device as element ofmechanical transmission in the case of manual actuation lies in the factthat, in this way, it is always possible to guarantee operation of thedevice also in the case of an accidental failure of the shape-memoryflexible cable.

It may be noted that in the case of the solution previously proposed,which is illustrated in FIG. 1, set between the cable 2 and the sheath 3is a spacer layer 106 made of synthetic material, which is joined to thesheath 3 and is fixed thereto. Said layer fulfils only a function ofspacer so that, during operation of the device, there is created arelative movement of the flexible cable with respect thereto.

In the case of the invention, instead, there is proposed an actuatordevice that is substantially similar to the one illustrated in FIG. 1,with the difference, however, that the flexible cable has a structure ofthe type illustrated in FIG. 2. In this FIG., the parts corresponding tothe ones of FIG. 1 are designated by the same reference numbers. As maybe seen, also according to the present invention there is provided theflexible cable 2 made of shape-memory material, with the correspondingflexible sheath 3, and a spacer layer 106, which in the case illustratedconsists of a metallic sheathing or hose.

The difference with respect to the solution previously proposed andillustrated in FIG. 1 lies in the fact that in this case, above thecable made of shape-memory material 2 is moulded a coating layer 110,which adheres to the shape-memory cable 2 and is chosen between theelastomer/silicone or synthetic material such as to favour both coolingof the cable 2 after cessation of the passage of electric current andthe return of the cable 2 to its resting configuration as a result ofthe elastic return of the coating 110.

As already mentioned, preferably the coating 110 is moulded over thecable 2 by means of an operation of co-extrusion of the materialconstituting the cable 2 and of the coating 110. In other words, duringthe production process, the cable 2 and the corresponding coating 110are obtained simultaneously by means of a process of co-extrusion, whichhas the advantage of enabling the desired structure to be obtained witha single operation, without any need for additional assembly operations.

As already mentioned, the coating 110, which is adherent to the cable 2,performs the function of a spring distributed longitudinally, which issubject to a compression when the cable 2 is shortened following uponthe its activation and consequently favours return of the cable to theresting position as a result of its elastic return.

As already mentioned above, the configuration of the shape-memory cablecan be any whatsoever. It is moreover possible to co-extrude a number ofshape-memory cables inside the same coating. Of particular interest is aU-shaped configuration of the cable, with a forward stretch and a returnstretch and the two ends of the cable that are adjacent to one another,which, among other things, enables the advantage of a convenientelectrical connection of the cable to the electrical-supply means.

Of course, without prejudice to the principle of the invention, thedetails of construction and the embodiments may vary widely with respectto what is described and illustrated purely by way of example, withoutthereby departing from the scope of the present invention.

1. An actuator device, comprising: a cable, having one end connected toa controlled member, and a sheath, inside which there is mounted thecable, in which at least one portion of the cable consists of ashape-memory material, which is able to undergo a variation of shapefollowing upon heating, in order to control the controlled member, inwhich said sheath is mounted with respect to a fixed supportingstructure so as to be free to be displaced longitudinally only in thedirection of actuation of the controlled member, and in which moreoverthe aforesaid sheath is coupled to the controlled member so as to beable to transmit directly thereto a displacement in the aforesaiddirection of actuation and to be, instead, uncoupled from the controlledmember in the event of a movement in the direction opposite to thedirection of actuation, in such a way that said actuator is able to beused both via manual actuation, using the sheath as element ofmechanical transmission, and exploiting the variation of shape of theshape-memory cable, which can be obtained via its heating, wherein saidcable is provided with a coating of elastomer/silicone or syntheticmaterial moulded thereon and adherent thereto, which is elasticallydeformed when the shape-memory cable is activated, so as to favourreturn of the shape-memory cable to its resting position both on accountof its elastic return and in so far as it accelerates cooling of theshape-memory cable after an activation.
 2. The actuator device accordingto claim 1, wherein said coating is obtained by means of a process ofco-extrusion with the shape-memory cable.
 3. An actuator device,comprising: a flexible cable, having one end to be connected to acontrolled member, and a flexible sheath, inside which there is mountedthe flexible cable, wherein at least one portion of the flexible cableconsists of a shape-memory material, which is able to undergo avariation of shape following upon heating, in order to control thecontrolled member, wherein said flexible cable is provided with acoating of elastomer or synthetic material moulded thereon and adherentthereto, which is elastically deformed when the shape-memory cable isactivated, so as to favour return of the shape-memory cable to itsresting position both on account of its elastic return and insofar as itaccelerates cooling of the shape-memory cable after an activation,wherein said coating constitutes a longitudinally distributed springwhich is subject to compression when the flexible cable is shortened dueto an activation of the shape-memory material so that the coatingfavours return of the shape-memory cable to its resting position uponactivation, and wherein the material of the coating favours the coolingof the flexible cable, whereby the return of the cable to its restposition is favoured.
 4. The actuator device according to claim 3,wherein said coating is obtained by means of a process of co-extrusionwith the shape-memory cable.
 5. The actuator device of claim 3, whereinsaid sheath can be mounted with respect to a fixed supporting structureso as to be free to be displaced longitudinally only in the direction ofactuation of the controlled member, and wherein the aforesaid sheath canbe coupled to the controlled member so as to be able to transmitdirectly thereto a displacement in the aforesaid direction of actuationand to be, instead, uncoupled from the controlled member in the event ofa movement in the direction opposite to the direction of actuation, insuch a way that said actuator device is able to be used both via manualactuation, using the sheath as element of mechanical transmission, andexploiting the variation of shape of the shape-memory cable, which canbe obtained via its heating.
 6. The actuator device of claim 3, whereina plurality of flexible cables are provided inside said coating.
 7. Theactuator device of claim 3, wherein said cable has a U-shapeconfiguration with two adjacent ends.